Computers such as conventional personal computers often utilize a time-consuming initialization procedure in order to load and initiate a computer operating system. The operating system for a computer is typically stored on some type of rotating non-volatile media such as a magnetic hard disk. However, the computer's microprocessor executes instructions only from addressable memory such as DRAM or some other type of volatile, electronic memory. In order to initialize this addressable memory, a small amount of non-volatile boot-up memory is typically provided in an EPROM (electronically programmable read-only memory) or similar device. This memory contains code for reading some initial portion of the operating system from the hard disk and loading it into DRAM. This portion of the operating system is then responsible for loading and initializing remaining portions of the operating system. This process is referred to as "booting" the operating system.
After a computer initializes itself or "boots," it is usually in a default state, ready for a user to initiate some program or process. In most cases, the computer is in the same state after every initialization, regardless of a user's past activities. That is, the computer does not "wake up" at the same point at which it was turned off. Rather, the user must reload any applications, documents, or files he or she wishes to use. This can be a significant inconvenience. If a user wishes to turn off his or her computer at the end of a workday, the user must save all work, exit all programs, and shut the computer down. At the beginning of the next day, the user must restart the computer, wait for it to boot, load any applications that were in use the day before (such as email programs, word processing programs, Internet browsers, etc.). Each application typically initializes itself to a default state, and the user must take further steps to load any documents or files that he or she was working with. Assuming, as an example, that the user was revising a text document, the user must load a word processor, load the appropriate document into the work processor, and also attempt to find the place in the document where work was interrupted the day before.
It would be much easier for the user if the computer would simply restart at the same point at which it was turned off. In fact, some computers are able to do this. When using such a computer, a user simply initiates a "hibernate" mode when it is time to turn the computer off. The term hibernate indicates that power is turned off in such a way that the computer is "paused." Thus, when the computer is turned back on, it resumes operation at the same point at which it was turned off. While the computer is turned off power is removed from all or at least most components of the computer.
To hibernate, the computer saves its entire volatile operating state to non-volatile storage (hard disk). Specifically, the computer saves the contents of all volatile DRAM (dynamic random-access memory), all pertinent state information from the computer's microprocessor, and volatile state information from peripheral components within the computer such as video drivers, printer drivers, etc. When the computer is turned back on, it automatically restores the memory contents and other saved state information. This avoids a lengthy boot process and allows a user to begin work immediately, without reinitializing application programs and documents.
"Hibernation" or "sleep" modes have been implemented primarily in portable computers. One reason for this is that such computers are typically "closed" from a hardware standpoint, meaning that computer hardware exists in a known and constant configuration--it cannot be changed or significantly reconfigured by a user. The code that implements the hibernation function resides in EPROM along with boot code. When it is time for hibernation, the processor jumps to code within the EPROM that is tailored very specifically to the known hardware of the computer. The EPROM code knows exactly what type of hard disk it needs to write to and exactly what internal peripherals need to have their states saved. Furthermore, the EPROM hibernation code can be written so that its execution does not affect the contents of DRAM, which must be saved to disk in an unaltered state. The problem with this approach is that it must be customized for every hardware configuration. For this reason, it has not been widely used. Most desktop computers do not provide a hibernation function.